1. Field of the Invention
The present invention relates to impact tools, for example fastener driving tools and hammer tools (e.g. rotary hammer tools or hammer drills). The invention is particularly relevant to fastener driving impact tools in which the fasteners include nails (i.e. nailers), but the invention also concerns other types of impact tools, and impact tools for other types of fasteners, including pins, staples, etc.
2. Description of the Related Art
Many impact tools include a driver that is propelled rapidly against a fastener to drive a fastener from the tool into a workpiece. The driver may comprise a piston, or a ram (impact member), for example. The driver may be propelled in any of a variety of ways, including (but not limited to) pneumatically, by combustion, by means of a strap or chain, by means of a separate piston, or by means of one or more flywheels, for example. However, whatever the manner of propelling the piston, the tool will normally need to include a resilient end stop—often termed a “bumper” or “buffer”—to halt the forward motion of the driver once the fastener has been driven from the tool. In some tools, the resilient end stop may be utilized every time the driver drives a fastener, and in other tools the resilient end stop may be provided as a back-up that is used only in the event of a failure of another component of the tool.
U.S. Pat. No. 4,042,036 discloses an electric impact tool having a pair of motor-driven counter-rotating flywheels arranged to propel a ram into engagement with a fastener to drive the fastener from the tool. A nose piece of the tool includes an energy-absorbing monolithic cushion to receive and absorb some of the excess kinetic energy of the ram as it nears completion of its work stroke.
U.S. Pat. No. 3,403,600 discloses a pneumatic fastening machine operated by compressed air controlled by a trigger actuated valve. The machine includes a piston axially movable in a cylinder, and the upper end of a driving member is fixed to the piston, with the remainder of the driving member extending downwardly from the piston. A valve member formed of resilient material, and having an opening, receives the drive member in the opening. An elastic sealing ring is disposed between a peripheral surface of the valve member and the inner surface of the cylinder. The valve member has an inclined peripheral surface carrying a metal ring, to press the sealing ring into engagement with a fixed member at the bottom of the cylinder. This action causes the elastic ring to expand and to be pressed against the inner surface of the cylinder when the piston moves the valve member axially downwardly at the end of the driving stroke.